1. Field of the Invention
Apparatuses consistent with the present invention relate to a radio frequency (RF) filter and a digital broadcast receiving tuner, and an RF signal processing device using the RF filter. More particularly, apparatuses consistent with the present invention relate to an RF filter, and a digital broadcast receiving tuner and an RF signal processing device using the RF filter in which band pass filtering can be performed on only a signal having a predetermined frequency or less to supply the filtered signal to a mixer.
2. Description of the Related Art
With development of electronic techniques, various systems for transmitting and receiving signals in a broadband have been realized and are being used. An example of those systems is a digital broadcast system.
In case of a broadband frequency signal processing system, when a user selects a specific frequency channel which the user wants to receive, the system receives signals through the selected channel. In this case, the harmonics of the channel also may be received as noise.
When a channel of 100 MHz is selected, a signal of 300 MHz, which is the third harmonic component of the selected channel, may be mixed with a local oscillator (LO) spectrum of 300 MHz to be converted to 100 MHz. A ratio of an actually wanted signal to noise may be reduced.
FIG. 1 is a graph illustrating an output power characteristic of an RF signal processing device according to the related art. Referring to FIG. 1, harmonic noise components are more than actually wanted signal components in the power spectral density.
In order to solve this problem, an attempt to realize a passive filter using various kinds of external elements, such as a varactor diode and an inductor, was made for removing harmonics. More specifically, a varactor whose capacitance varies was used to change an oscillation frequency according to voltage variation, thereby performing filtering on n-th (3rd, 5th, 7th, 9th, or the like) harmonics of an input signal. In this way, an amount of inflow noise during a mixing operation of a mixer was reduced.
In this case, however, various kinds of external elements are required, resulting in a large size of a module. Further, a feedback path is required to change an input voltage of the varactor, causing power consumption to increase.
In particular, it is required to perform filtering on all of signals in a broad band (about 48 MHz to 870 MHz), resulting in a large amount of power consumption.